If my period came on on jun 15th and I've had sex on July 5th with an expected period on the 13th of July but it didn't come on until the 26th lasted for four days I've have sex on the 31st and the 6th of August... went to the doctor yesterday and the doctor said that I was 3 weeks pregnant so my question is around what time did I get pregnant if my conception date is the 10th but I'm 3 weeks ?

Calculating Conception dates is an inexact science. If you can pinpoint that you only had sex on the 31st and 6th, EITHER date is possible With the 31st the more likely

If you give me a due date, rather than having to sort out this riddle, I could give you an estimation of when you conceived. Remember though that conception is only an educated guessing game.